Answer:
There is now (as of DevForce version 3.4.0). GetEntityGraph (a new method on the PM) will enable you to obtain a collection of the entire graphs of specified entities, which collection can then be saved, or imported from one PM to another. GetEntityGraph only works with entities in the cache.
This is the signature:
/// <summary>
/// Given any entity or entities in a graph, collects and retrieves all
/// related entities in the graph. This is a cache-only operation.
/// </summary>
/// <param name="pEntityRoots">A list of entities used as the starting point for retrieving all other related entities</param>
/// <param name="pEntitySpans">One or more <see cref="EntitySpan"/>s</param>
/// <param name="pRowState">RowState of entities to return</param>
/// <returns>A list of related Entities</returns>
/// <exception cref="ArgumentNullException">Thrown if pEntityRoots and/or pEntitySpans is null.</exception>
/// <exception cref="ArgumentException">Thrown if the type in a span does not have a matching type in one of the roots.</exception>
public EntityList<Entity> GetEntityGraph(
IEnumerable<Entity> pEntityRoots,
IEnumerable<EntitySpan> pEntitySpans,
DataRowState pRowState)